1. Technical Field
This disclosure is generally input control to handle input current, and in particular to handle inrush current, and under voltage and over voltage conditions. Such may, for example be useful in a wide variety of devices or systems, particularly those with relatively large input capacitors, for example power converters, such as regulated switched mode power converters with bulk input filter capacitors.
2. Description of the Related Art
Power converters are used to transform electrical energy, for example converting between alternating current (AC) and direct current (DC), adjusting (e.g., stepping up, stepping down) voltage or potential levels and/or frequency.
Power converters take a large variety of forms. One of the most common forms is the switched-mode power converter or supply. Switched-mode power converters employ a switching regulator to efficiently convert voltage or current characteristics of electrical power. Switched-mode power converters typically employ a storage component (e.g., inductor, transformer, capacitor) and a switch that quickly switches between full ON and full OFF states, minimizing losses. Voltage regulation may be achieved by varying the ratio of ON to OFF time or duty cycle. Various topologies for switched-mode power converters are well known in the art including non-isolated and isolated topologies, for example boost converters, buck converters, synchronous buck converters, buck-boost converters, and fly-back converters.
In the interest of efficiency, digital logic technology is employing ever lower voltage logic levels. This requires power converters to deliver the lower voltages at higher currents level. To meet this requirement, power converters are employing more energy efficient designs. Power converters are also increasingly being located in close proximity to the load in as point of load (POL) converters in a POL scheme. These power converters must generate very low voltage levels (e.g., less than 1V) at increasingly higher current levels (e.g., greater than 10 A). These relatively high current levels may be difficult to achieve with a single power converter.
Manufacturers are also increasingly employing POL schemes in light of the widely varying voltage requirements in modern systems (e.g., computer systems). A POL scheme may be easier to design and/or fabricate, take up less area, and/or produce less interference than employing multiple different power buses. The POL schemes typically employ one or two power buses with a number of POL regulators located close to specific components or subsystems to be powered, for example microprocessors, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), volatile memory. The POL regulators adjust voltage to supply localized busses feeding the specific components or subsystems.
Many devices employ input capacitors. For example, switched mode power converters typically include a large internal bulk filter capacitor to filter the input power to reduce noise conducted out of the power converter 100, back upstream to the source of the input power. The input capacitor may also store and/or smooth input power.
However, upstream devices (e.g., power converters) may not be able to source or start up devices with large capacitances. Often times, upstream power converters are internally limited, and enter a “hiccup” mode or repeatedly restart when faced with a large capacitive load. Thus, various attempts have been made to design circuits which effectively limit inrush current.
Present approaches to controlling the capacitive inrush current of a device typically employ a series resistance or directly sensing the inrush current of the device through resistive sensing, magnetic sensing, or Hall effect sensing. These approaches to sensing the actual input current waveform lead to a substantial power loss, complicated designs, and/or high costs to address electrical isolation requirements, as well as slow transient response. For example, sensing an input current with a resistive element dissipates power and requires specific circuitry to amplify the sense signal and reduce common mode noise. Sensing with a magnetic element reduces power dissipation. However, such an approach adds significant cost, requires added circuitry to amplify the signal, and is only applicable in AC current sensing applications. Thus, this approach is only useful for very high AC current applications. Due to their low sensitivity Hall effect sensors likewise require added circuitry to amplify the signal and to reduce common mode noise.
Thus, the various approaches require a number of tradeoffs due to design issues. For example, approaches which employ a permanently placed resistor to limit inrush current suffer from a substantial decrease in efficiency. It is typically difficult to derive an accurate input current signal without degrading the overall efficiency. Signal integrity degradation resulting from common mode noise/current is also a problem. Additionally, a voltage shift of the signal down to the electrical circuit ground potential may occur in some designs. Further, many approaches have had difficulty in maintaining fast transient response.
Additionally, many applications require that voltage be maintained within an acceptable range. Thus, under voltage and over voltage conditions must be monitored and handled.
New approaches to handling inrush current, under voltage and over voltage monitoring are desirable.